From: balbi@ti.com (Felipe Balbi) To: linux-arm-kernel@lists.infradead.org Subject: [PATCH] i2c: omap: improve duty cycle on SCL Date: Thu, 18 Jun 2015 12:24:28 -0500 [thread overview] Message-ID: <20150618172428.GB27790@saruman.tx.rr.com> (raw) In-Reply-To: <5582678F.4010505@gmx.de> On Thu, Jun 18, 2015 at 08:39:11AM +0200, Michael Lawnick wrote: > Am 17.06.2015 um 17:38 schrieb Felipe Balbi: > >Hi, > > > >On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote: > >>Am 16.06.2015 um 21:17 schrieb Felipe Balbi: > >>>With this patch we try to be as close to 50% > >>>duty cycle as possible. The reason for this > >>>is that some devices present an erratic behavior > >>>with certain duty cycles. > >>> > >>>One such example is TPS65218 PMIC which fails > >>>to change voltages when running @ 400kHz and > >>>duty cycle is lower than 34%. > >>> > >>>The idea of the patch is simple: > >>> > >>>calculate desired scl_period from requested scl > >>>and use 50% for tLow and 50% for tHigh. > >>... > >>Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5? > >> > >>>PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT > >>> MIN. MAX. MIN. MAX. > >>>LOW period of the SCL clock tLOW 4.7 ? 1.3 ? ?s > >>>HIGH period of the SCL clock tHIGH 4.0 ? 0.6 ? ?s > >> > >>Your signal is in spec (0.85 ?s high, 1,65 low). > >>Maybe your TPS65218 is just buggy or signals are bad? > > > >yes, tps is buggy, it's written in the commit log itself. > > > > So I think it is unacceptable to change the adapters code violating > specification because some buggy device doesn't work properly. read the other thread and you'll see that it's not violating jack > This change for your device has chance to blow up many correctly > working ones. How ? -- balbi -------------- next part -------------- A non-text attachment was scrubbed... Name: signature.asc Type: application/pgp-signature Size: 819 bytes Desc: Digital signature URL: <http://lists.infradead.org/pipermail/linux-arm-kernel/attachments/20150618/2359f2bf/attachment.sig>
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From: Felipe Balbi <balbi@ti.com> To: Michael Lawnick <ml.lawnick@gmx.de> Cc: balbi@ti.com, wsa@the-dreams.de, Tony Lindgren <tony@atomide.com>, Nishanth Menon <nm@ti.com>, Dave Gerlach <d-gerlach@ti.com>, linux-i2c@vger.kernel.org, Linux OMAP Mailing List <linux-omap@vger.kernel.org>, Linux ARM Kernel Mailing List <linux-arm-kernel@lists.infradead.org> Subject: Re: [PATCH] i2c: omap: improve duty cycle on SCL Date: Thu, 18 Jun 2015 12:24:28 -0500 [thread overview] Message-ID: <20150618172428.GB27790@saruman.tx.rr.com> (raw) In-Reply-To: <5582678F.4010505@gmx.de> [-- Attachment #1: Type: text/plain, Size: 1659 bytes --] On Thu, Jun 18, 2015 at 08:39:11AM +0200, Michael Lawnick wrote: > Am 17.06.2015 um 17:38 schrieb Felipe Balbi: > >Hi, > > > >On Wed, Jun 17, 2015 at 01:09:53PM +0200, Michael Lawnick wrote: > >>Am 16.06.2015 um 21:17 schrieb Felipe Balbi: > >>>With this patch we try to be as close to 50% > >>>duty cycle as possible. The reason for this > >>>is that some devices present an erratic behavior > >>>with certain duty cycles. > >>> > >>>One such example is TPS65218 PMIC which fails > >>>to change voltages when running @ 400kHz and > >>>duty cycle is lower than 34%. > >>> > >>>The idea of the patch is simple: > >>> > >>>calculate desired scl_period from requested scl > >>>and use 50% for tLow and 50% for tHigh. > >>... > >>Hmm, and what's about Philips I2C specification 2.1, Jan 2000, Table 5? > >> > >>>PARAMETER SYMBOL STANDARD-MODE FAST-MODE UNIT > >>> MIN. MAX. MIN. MAX. > >>>LOW period of the SCL clock tLOW 4.7 – 1.3 – µs > >>>HIGH period of the SCL clock tHIGH 4.0 – 0.6 – µs > >> > >>Your signal is in spec (0.85 µs high, 1,65 low). > >>Maybe your TPS65218 is just buggy or signals are bad? > > > >yes, tps is buggy, it's written in the commit log itself. > > > > So I think it is unacceptable to change the adapters code violating > specification because some buggy device doesn't work properly. read the other thread and you'll see that it's not violating jack > This change for your device has chance to blow up many correctly > working ones. How ? -- balbi [-- Attachment #2: Digital signature --] [-- Type: application/pgp-signature, Size: 819 bytes --]
next prev parent reply other threads:[~2015-06-18 17:24 UTC|newest] Thread overview: 16+ messages / expand[flat|nested] mbox.gz Atom feed top 2015-06-16 19:17 [PATCH] i2c: omap: improve duty cycle on SCL Felipe Balbi 2015-06-16 19:17 ` Felipe Balbi 2015-06-16 19:19 ` Felipe Balbi 2015-06-16 19:19 ` Felipe Balbi 2015-06-17 11:09 ` Michael Lawnick 2015-06-17 11:09 ` Michael Lawnick 2015-06-17 15:38 ` Felipe Balbi 2015-06-17 15:38 ` Felipe Balbi 2015-06-18 6:39 ` Michael Lawnick 2015-06-18 6:39 ` Michael Lawnick 2015-06-18 17:24 ` Felipe Balbi [this message] 2015-06-18 17:24 ` Felipe Balbi 2015-06-19 5:41 ` Michael Lawnick 2015-06-19 5:41 ` Michael Lawnick 2015-06-19 15:30 ` Felipe Balbi 2015-06-19 15:30 ` Felipe Balbi
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